Let’s be blunt

How do metal blades in wet shavers lose their sharpness so easily on human hair and how can I avoid this?

• Being related to a family that owns and operates a cutlery-grinding business, I’ve learned a few things about keeping cutting edges sharp: start with good steel, handle it carefully and dress, or cover, it frequently. If you do this, you can have knife edges that you can actually shave with – I’ve seen it.

“Losing the edge”, as it is known, is a bit of a misnomer. What actually happens is that the microscopically sharp extreme edge of the freshly sharpened blade gets bent or rolled over, largely depending on the item contacted. A butcher carving up a roast can therefore go a while if cutting through meat, but as soon as they strike a bone, it’s time to find the honing steel. This will restore the edge with a few strokes.

But back to the shaver: it is impractical to rehone the blade, so perhaps the problem can be addressed by making what is being cut as soft as possible. A nice soak in a hot shower or a minute with a hot cloth on the face before shaving might help the blade last longer.

• Wet shavers must maintain microscopically fine cutting edges to remain effective. Even razors with multiple square-ended blades rely on sharp corners, so erosion of just a fraction of a micrometre causes drastic blunting. The sharper the edges, the faster they erode.

It is a sort of surface tension effect: the atoms comprising any sharp edge are most exposed to chemical attack and poorly supported against abrasion. Suitably designed dry blades can sharpen in action by grinding each other, but that doesn’t work well in corrosive liquid. Certain metal surfaces can be protected by a layer of resistant oxide, but that works less usefully under water. Furthermore, wet muck between sliding surfaces forces blades apart, preventing crisp cutting and demanding frequent cleaning.

Jon Richfield, Somerset West, South Africa

• My dad used to work for a large razor blade manufacturer. He told me that the firm had done tests showing that by alternating blades, more clean shaves could be completed per razor than if you used the same blade every day.

He said this was why expensive cutthroat razors came in sets of seven – and why using a “magic pyramid” (popular in the 1970s), whereby a razor blade was placed under the pyramid for a few days and apparently resharpened itself, seemed to work.

David Clarke, Seaford, East Sussex, UK

Does any reader know why alternating blades makes each one last longer? – Ed

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